This application is based on Application No. 2001-162100, filed in Japan on May 30, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a throttle valve control device for an internal combustion engine in which the rotation of a motor corresponding to an amount of operation of an accelerator pedal is transmitted through a gear mechanism to a shaft of a throttle valve, which adjusts the amount of intake air sucked into the internal combustion engine.
2. Description of the Related Art
FIG. 7 is a cross sectional side view of a known throttle valve control device for an internal combustion engine. This throttle valve control device for an internal combustion engine includes a housing 1, a motor 2 provided in the housing 1, a small gear wheel 4 fixed to a rotating shaft 3 of the motor 2, an intermediate gear wheel 5 in mesh with the small gear wheel 4, a sector gear 6 in mesh with the intermediate gear wheel 5, a shaft 7 rotatably mounted on the housing 1 across an intake passage formed therein with the sector gear 6 fixedly attached thereto at its one end, a throttle valve 8 fixedly mounted on the shaft 7 for rotation therewith, a return spring 9 for urging the throttle valve 8 in its closing direction at all times through the shaft 7, and an opening sensor 10 fixedly attached to the shaft 7 on one side of the sector gear 6 opposite the throttle valve 8 for detecting the opening of the throttle valve 8.
FIG. 8 is a front elevation of the sector gear 6, and FIG. 9 is a cross sectional view along line IXxe2x80x94IX of the sector gear 6 of FIG. 8. The sector gear 6 is comprised of a generally sector-shaped core member 11 and a resin molded portion 13 with teeth 12 formed on the core member 11 by means of insert molding. The core member 11 is formed by pressing a metal sheet. The metal sheet is used for ensuring the proper strength of the sector gear 6.
FIG. 10 is a front elevation of a sector gear 15 of another example, and FIG. 11 is a cross sectional view along line XIxe2x80x94XI of the sector gear 15 of FIG. 10. This sector gear 15 is formed on the whole by sinter molding a ferrous material.
With the known sector gear 6 as described above, the resin molded portion 13 having the teeth 12 is formed on the core member 11 by means of insert molding, but in this case, there arises a problem that a molding sink 16 as shown by a dotted line in FIG. 12 is caused on the tooth surfaces 12a of the teeth 12 under the action of shrinkage occurring upon hardening of the resin, whereby the tooth surfaces or crest surfaces 12a are caused to incline in a diametral or radial direction from a horizontal line, as illustrated in FIGS. 13A and 13B.
In addition, with the sector gear 15 which on the whole is molded by sintering, inclinations of the tooth surfaces of the teeth 12 can be avoided, and hence the sector gear 15 is improved in accuracy and reliability, but gives rise to another problem that the weight of the sector gear 15 is substantially increased.
The present invention is intended to obviate the problems as referred to above, and has for its object to provide a throttle valve control device for an internal combustion engine which has a sector gear with improved teeth accuracy by preventing inclinations of the teeth surfaces.
Bearing the above object in mind, the present invention resides in a throttle valve control device for an internal combustion engine comprising a motor and a sector gear operatively connected with the motor for driving a shaft having a throttle valve fixedly mounted thereon, the sector gear including a sector-shaped core member and a resin molded portion with teeth formed on the core member by insert molding. The throttle valve control device is characterized in that the core member has a support portion with a curved surface formed to extend along bottoms of the teeth and project in an axial direction.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.